A full frame image sensor is basically a two dimensional array of pixel sensing elements of size x columns by y rows. The image sensors capture light and stores the light captured in the individual pixel sensors. The pixels are vertically shifted down each column in parallel by one row, with the last row being shifted out and filling a horizontal shift register. These pixels in the horizontal shift register are then shifted out one at a time (serially) until the horizontal shift register is completely empty. At this time, the sensor is ready to fill the horizontal shift register again, and the process of parallel to series shift explained above is repeated one row at a time until all rows of the sensor have been transported out of the sensor.
In typical high resolution image sensors, some of the pixels of the image sensing array provide corrupted data, which can be classified into three different types: pixel, column, and cluster defects. These defects are often characteristics of the device and are formed during the manufacturing process. The defects are typically mapped during the manufacturing process, but in some cases additional defects are also detected when the sensors are assembled into the final product, such as a digital camera. For example, the temperature or the clock and timing characteristics of the electronics controlling the sensor can cause additional defects. Also, during the product assembly, dust, dirt, scratches, etc. may be introduced.
With full frame image sensors, there is often a problem where there are one or more defective pixels in a column. Such a defective pixel will cause corrupted data in the digital image after it is read out of the image sensor. Depending on the cause of the defect, the column might be only partially corrupted. For example, the lower portion of the column could provide proper data while the upper portion provides corrupted data. To produce the highest quality image, this partial column defect needs to be identified, so that the data provided by the defective upper portion can be concealed, while the data from the lower portion is utilized to create the final image.
What is needed is a method of quickly and automatically identifying partial column defects in an image sensor, so that an effective map of the defective pixels can be provided.